The Sun unleashed an M-2 (medium-sized) solar flare, an S1-class (minor) radiation storm and a spectacular coronal mass ejection on June 7, 2011. The large cloud of particles mushroomed up and fell back down looking as if it covered an area of almost half the solar surface. A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up a sixth of the total energy output of the Sun each second. Solar flares strongly influence the local space weather in the vicinity of the Earth. They can produce streams of highly energetic particles in the solar wind, known as a solar proton event, or coronal mass ejection. These particles can impact the Earth's magnetosphere and cause a geomagnetic storm. A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a disturbance in the interplanetary medium. A geomagnetic storm is a major component of space weather and provides the input for many other components of space weather, and present radiation hazards to spacecraft, astronauts and cosmonauts. The current flare event is moving at 1400 km/s according to NASA models. The flare event should deliver a glancing blow to Earth's magnetic field during the late hours of June 8th or June 9th. High-latitude sky watchers should be alert for auroras when the it arrives.

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What is happening is a coronal mass ejection. The outer solar atmosphere, the corona, is structured by strong magnetic fields. Where these fields are closed, often above sunspot groups, the confined solar atmosphere can suddenly and violently release bubbles of gas and magnetic fields called coronal mass ejections. A large ejection can contain a billion tons of matter that can be accelerated to several million miles per hour in a spectacular explosion. Solar material streams out through the interplanetary medium, impacting any planet or spacecraft in its path.

In 1958 you could not tell that a solar storm was underway by looking at the bars on your cell phone; cell phones did not exist. Even so, people knew something big was happening when Northern Lights were sighted three times in Mexico. A similar storm now would be noticed by its effect on cell phones, GPS, weather satellites and many other modern technologies.

In September 1859, the largest recorded geomagnetic storm occurred. From August 28 until September 2, 1859, numerous sunspots and solar flares were observed on the Sun, the largest flare occurring on September 1. This is referred to as the 1859 solar superstorm or the Carrington Event. It can be assumed that a massive coronal mass ejection, associated with the flare, was launched from the Sun and reached the Earth within eighteen hours — a trip that normally takes three to four days. Telegraph wires in both the United States and Europe experienced induced emf, in some cases even shocking telegraph operators and causing fires. Auroras were seen as far south as Hawaii, Mexico, Cuba, and Italy.

In March 1989 a severe geomagnetic storm caused the collapse of the Hydro-Québec power grid in a matter of seconds as equipment protection relays tripped in a cascading sequence of events. Six million people were left without power for nine hours, with significant economic loss. The storm even caused auroras as far south as Texas. The geomagnetic storm causing this event was itself the result of a coronal mass ejection, ejected from the Sun on March 9, 1989.

Ice cores show evidence that events of similar intensity recur at an average rate of approximately once per 500 years. Since 1859, less severe storms have occurred in 1921 and 1960, when widespread radio disruption was reported.